E149 ASE High Availability Using Sybase Rep Server

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E149 ASE High Availability Using Sybase Rep
Server

• Mano Malayanur
• Manager, Database Engineering
• Fannie Mae
• mmano_at_erols.com

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HIGH AVAILABILITY IMPLICATIONS

• High MTBF, Low MTTR Required
• Must Not Break Often When Broken, Fix Must Be
  Quick
• Planned Or Not, Long Outage Not Allowed
• How Will You Upgrade Your ASE To 12.5?
• Availability End-To-End Is What Matters, Not
  Individual Components
• Not OK To Say, But The Server Is Up! When DB Is
  Off-line Due To Error 605

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HIGH AVAILABILITY RELATED CONCEPTS

• 24x7 (Or Continuous Availability)
• Rolling Production
• Active-Active Configurations
• Disaster Recovery (Or Site Disaster Contingency)
• Shared Nothing Architectures

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HIGH AVAILABILITY REQUIREMENTS

• Redundancy For Hardware Failures
• Maintenance Windows (Platform, HW)
• Fast, Automated, Preferably Transparent Fail Over
  and Fail Back
• Other Requirements
• Disaster Recovery Capability
• High Return On Investment (Use Redundant Systems)
• Scalability Add Performance On Demand

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HIGHLY AVAILABLE DATABASES SPECIAL REQUIREMENTS

• Data Persistence Data Must Be Available On
  Redundant System After Fail Over
• Unlike For Web Servers, Application Servers
• Protection From Data Corruption, Damage
• Cause High MTTR
• DB Maintenance Windows
• DBCCs, Index Rebuilds, SW/ASE Upgrades
• Bottom Line High Availability For DBs Is Much
  Harder Than For Other n-Tier Components

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CLUSTERING FOR DATABASE HIGH AVAILABILITY

• Meets Redundancy, Scalability, High ROI, And
  Quick Fail Over Requirements
• Does Not Meet Disaster Recovery Requirement
  (Distance Limits Apply)
• Does Not Meet Any Database HA Requirements (It Is
  The Same Data!)
• Bottom Line Clustering Alone Does Not Support DB
  High Availability

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REP SERVER FOR ASE HIGH AVAIL. NORMAL
CONFIGURATION
User Sessions
Active ASE
Standby ASE
Rep Server
Stable Device
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REP SERVER FOR ASE HIGH AVAIL. ALTERNATIVE
CONFIGURATION
User Sessions
ASE In Maintenance
Active ASE
Rep Server
Stable Device
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NORMAL OPERATION

• Rep Server Configured As Warm Standby
• Users Connect To The Active ASE
• DB Maintenance Done On Standby ASE
• Rep Server Connections Suspended If Needed During
  Standby ASE Maintenance
• Active and Standby ASEs Swapped Using Rep Server
  Switch Active Commands
• Periodic Swaps Boost Confidence In Standby ASE
  Config And Swap Process

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WARM STANDBY SWAP PROCESS

• Process
• Ensure Rep Server Queues Are Small
• Bring Down Apps On Active ASE
• Lock Logins Kill Extant User Sessions Drain Rep
  Server Queues Quiesce Rep Server
• Run Switch Active Commands For Each DB
• Unlock Logins On New Active ASE
• Distribute New Interfaces File If Needed
• Restart Apps (They Will Connect To New ASE)

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WARM STANDBY SWAP CONSIDERATIONS

• Sybase Active Switch Can Be Used ISO Interfaces
  File Push
• Other Config Changes May Be Needed
• Swap Aware Apps Faster Swaps
• LDAP ISO Interfaces File Push (Requires Sybase
  Open Client 12.5 And LDAP Use)
• Dovetails Beautifully With Clustering, Providing
  A Robust Overall Solution
• Easily Modified For Disaster Situations

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REP SERVER VS. HARDWARE REPLICATION

• Hardware Replication
• Transaction Unaware
• No Distance Limit WAN OK
• No Support For DB Maintenance
• Depends (Sync? Async?)
• No Protection From Corruption
• Replication Simple Since It Occurs At Block Level
• Synchronous Replication Possible

• Rep Server
• Transaction Aware
• No Distance Limit WAN OK
• Excellent Supp. For DB Maint.
• Supported By Sybase Inc.
• Excellent Protection From Corruption
• Replication Complex And Prone To Issues
• Asynchronous Replication Only

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REP SERVER AND ASE HIGH AVAILABILITY REQUIREMENTS